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原始链接: https://news.ycombinator.com/item?id=41238102

最近的研究表明，地球总水量的大约一半位于地幔内。这一发现挑战了之前关于地球上水分布的假设，因为目前地幔中的水量相当于所有海洋中水量的总和。虽然地幔中的水在维持地球的热平衡方面发挥着至关重要的作用，但由于其难以捉摸的性质，它给理解地质过程带来了困难。此外，随着时间的推移，到达地表的地幔水量是不确定的，尽管它可能是通过地热和构造活动发生的。在地质时期，地球表面的水的很大一部分可能由于蒸发而逃逸到太空中。这些发现的影响仍然是科学家们正在进行的研究和讨论的主题。

NB: The infographic and articles are based on a 1993 publication.

More recent research, from about 2017, suggests that there's about as much water in Earth's mantle as in all the oceans, so we either need another drop roughly the volume of the first, or the second drop should be greatly expanded.

See: "There’s as much water in Earth’s mantle as in all the oceans" (2017) <https://www.newscientist.com/article/2133963-theres-as-much-...>

The USGS is citing a 1993 publication, Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), Water in Crisis: A Guide to the World's Fresh Water Resources (Oxford University Press, New York) (see the detail links from the submitted article).

That said, water remains a precious resource, and fresh surface water all the more so.

Edit: /double the size/s/size/volume/ above, for clarity.

I don't think it's "hydrogen and oxygen ions"; that doesn't really meet the definition of water. I'd assume it's more like ebsom salts, where H2O is a part of the crystalline structure of the chemical compound. If you heat up epsom salts enough then the bonds are broken and steam is released.

> Hydrogen and oxygen ions inside minerals in rock is far too much of a stretch of imagination to call as water.

Agreed and to follow that thread to the end: We can't impact that water in a meaningful way.

We can't pollute it in dozens of ecosystem-altering ways.

We can't alter it's ability to host systems that sustain life.

We can't bulk-melt the frozen part & in turn alter the salinity + elevation of a liquid part.

We can't pump dry the parts that we desperately need to remain where they are.

> More recent research, from about 2017, suggests that there's about as much water in Earth's mantle as in all the oceans, so we either need another drop roughly the size of the first, or the second drop should be greatly expanded.

Specifically: given that the volume of a sphere is 4/3πR^3, doubling the volume is equivalent to increasing the radius by ~26%.

Does any of that water, though, ever make it onto the Earth's surface? I'm guessing not, or only miniscule amounts over geologic time through volcanism.

For all intents and purposes, I think only counting "surface" water is more useful and intuitive. It's essentially any water that can participate in the hydrologic cycle on Earth, and that water locked beneath the crust doesn't really "matter" for what I think the intended purpose of this graphic is.

The fundamental problem with complex phenomena is in defining the domain(s) of interest.

If we want to talk about the total amount of H2O around, on, or in the Earth then inclusion makes sense.

If we want to talk about water interacting with the surface environment (atmospheric, sea, ice cap, fresh, and subsurface aquifers and tectonic water), then splitting those into distinct categories probably also makes sense. In which case we can also show the subsurface water.

How much mantle water does make it to the surface over time is a good question. I've no idea though I'd suspect that some does through geothermal and tectonic activity. The more interesting question might be how we'd determine this (all but certainly through isotopic composition), and if a net flux could be determined.

Over geological time, additional reservoirs of water are significant simply because surface water boils off into space over time, with estimates I've seen of up to 25% of Earth's original allotment having done so over 4.5 billion years or so. As the Sun eventually grows warmer, this rate will increase. At the same time, tectonic activity will slow.

Note that there's a fair bit of water transport through the lower crust / upper mantle as oceanic plates subduct under continental plates, with the water absorbed into the oceanic plates playing a major role in volcanism at those plate boundaries, e.g., along the "Rim of Fire" surrounding the Pacific basin.

Earth is lucky to have a strong magnetic field and ozone layer limiting the loss of hydrogen to the solar wind. Mars, for example, has lost much more of its allotment.

The article has a strong focus on "available to humans" and "that humans depend on". Many of the water beneath the crust is exactly that, pumping it up is an important source of drinking water. (In my country, the Netherlands, it's the primary, almost only, source of drinking water)

It does separate liquid fresh water from surface lakes and rivers which makes me believe the middle ball includes reasonably accessible ground water.

An interesting point, perhaps it's just me, but my initial reaction to this was that, for purposes of comparison, the volume of "usable" or maybe inhabitable land be measured instead, as opposed to the volume of the entire planet including mantle, core, etc. this graphic seems very prone to misinterpretation and usage as a memetic weapon against globalization, as it is.

It's similarly misleading to color coding a map of a nation's or a region's land area to show how the people who occupy various parts of that land area voted in an election. The graphic representation tells a story about the land that deceptively implies facts about the people that are not true.

The Netherlands doesn't pump water from beneath the crust! Groundwater is included in the larger freshwater sphere. Water in the mantle would be an additional sphere (not sure if it's freshwater or saltwater).

TIL. I did not get that that from the article. Thanks for correcting me.

I simply presumed that water that's pumped from layers 100m or lower below the surface, water that's sometimes 10.000 years "old", wasn't surface water. But it makes sense to lump it in there too.

PFAS have reportedly contaminated water everywhere on Earth including the water in springs, confined aquifers, and even the rain that falls.

Is the water pumped from beneath the crust in the Netherlands poisoned too or have you guys got the last of the good stuff?

We don't have access to any part of the planet below a depth of 2.5 miles, so the image should compare the volume of accessible water to the volume of accessible Earth, except then it would fail in its dishonest mission to make people say "gosh that sphere looks relatively small compared to the other sphere, I must restrict myself to ten-second showers."

Even if it was accessible water to accessible non-water I don't really see how the metric is relevant in any decision making. Is it warning against a half-baked plan to mix water with every available cubic meter of soil or rock? Because there wouldn't be enough water to do that crazy thing? Thanks, I'll bear that in mind.

You seem really upset about what to me looks like a quite neutrally presented fact. There are lots of interesting aspects to this picture which don't have anything to do with criticizing you or the length of your morning shower.

It’s just an interesting infographic that is factually correct. You can disagree that the chosen facts are relatively the best ones, but, not everything has to have an agenda. Calling facts dishonest because they make you uncomfortable is what I consider yucky.

>We don't have access to any part of the planet below a depth of 2.5 miles

Given how many miles I can travel over land or through the air, 2.5 miles _into_ the earth is amazingly shallow in similar ways to how the article already anticipated my amazement of how small the spheres of water were.

> or the second drop should be greatly expanded.

The second drop is called "liquid fresh water".

I'm not sure if I would want to categorize the water in the mantle as either "liquid" or "fresh". Most of that stuff is way above the critical point, not to mention saturated with rocky salts.

I long assumed that the Earth is a "water planet" because water is mostly what you see from a distance. It wasn't until I did the math that I realized that is really about wet rocks in space vs dry rocks in space.

Earth isn't made of water, it's just a damp rock. Or a bowling ball that you squirted a dozen times with a spray bottle.

Well, the spray bottle was more to spread the water out into a thin layer as opposed to something like crashing an icy asteroid in at one spot.

I have a mental image of a gigantic cosmic being grabbing the Earth, wiping off the wet stuff with a rag, and bowling it at Proxima Centauri.

There was an old sci-fi trope that the reason aliens attack earth is to get at our water.

The problem with that was, 1. there are better sources of water (the oort cloud) and 2. they aren't stuck in an gravity well.

This didn't sound right, so I did the math.

The volume of all water is 1,386,000,000 km^3, which is then 1.386e+21 liters, or right about the same number of kilograms.

The mass of Earth is about 5.972e+24 kg. So the percent fraction by mass is 0.0232%.

A "drop" is typically estimated at 1/20th of one mL, which is then 0.05 grams. We can estimate the mass of a small-ish bowling ball at 5kg, or 5000 grams. 0.05 / 5000 * 100 = 0.001%.

So it's an order of magnitude shy, but that's still closer than I expected! It's about 1 ml of beer on a bowling ball - a small splash. Or maybe a very large drop.

Lava is not really representative of the Earth as a whole, as it turns out. The mantle (which is the vast majority of Earth's volume) isn't a liquid, it's a squishy deformable solid. Magma that comes from the mantle is only liquid because of the removal of pressure or the addition of water; it wasn't liquid down there. And a lot of lava comes from crustal melting, not mantle material.

Earth as a whole has a density about 5.5x that of water.

The picture already answers this question. If the earth was a bowling ball the blue sphere would be much bigger than a single drop, maybe slightly bigger than a popping boba, the size of a small grape?

The ballpark math is easy to do in your head too. The diameter of Earth is 8,000 miles, and the deepest point in the ocean, the Mariana Trench, is only 7 miles deep. It's immediately apparent that the oceans are tiny by comparison to the rest of the mass that is Earth.

This was analyzed and the results were mixed...

https://billiards.colostate.edu/bd_articles/2013/june13.pdf

>So, based on the data, just how smooth is a CB? And how does this smoothness compare to the surface of the Earth? The highest point on earth is Mount Everest, which is about 29,000 feet above sea level; and the lowest point (in the earth’s crust) is Mariana’s Trench, which is about 36,000 feet below sea level. The larger number (36,000 feet) corresponds to about 1700 parts per million (0.17%) as compared to the average radius of the Earth (about 4000 miles). The largest peak or trench for all of the balls I tested was about 3 microns (for the Elephant Practice Ball). This corresponds to about 100 parts per million (0.01%) as compared to the radius of a pool ball (1 1/8 inch). Therefore, it would appear that a pool ball (even the worst one tested) is much smoother than the Earth would be if it were shrunk down to the size of a pool ball. However, the Earth is actually much smoother than the numbers imply over most of its surface. A 1x1 millimeter area on a pool ball (the physical size of the images) corresponds to about a 140x140 mile area on the Earth. Such a small area certainly doesn’t include things like Mount Everest and Mariana’s Trench in the same locale. And in many places, especially places like Louisiana, where I grew up, the Earth’s surface is very flat and smooth over this area size. Therefore, much of the Earth’s surface would be much smoother than a pool ball if it were shrunk down to the same size.

Not completely accurate, it depends on your definition of smoothness. The Earth scaled down to the size of a billiard ball would have a texture more like sandpaper, certainly not what most people would consider smooth.

It's fun to scale down the Earth's depth to a 8 metre long measuring tape on the floor and then having kids guess things lik, how deep is the ocean, how deep is the deepest hole we've ever dug, how high is the atmosphere.

Adding in how far of a drive is it to X place or how far of a walk is it, is also fun.

> Earth isn't made of water, it's just a damp rock. Or a bowling ball that you squirted a dozen times with a spray bottle.

Yeah, the image with the oceans being dry is wow-inducing... On further thought, of course it'd be very close a sphere, because gravity forces it to be. A sphere where e.g. a slice of it is water (imagine a clementine with one of its segments being water) would be very wobbly if even possible at all..

Yup, the mere fact that we can have oceans and continents on a planet means we can only have so much water, lest we become a water world or something more like mars.

I do wonder if the OP includes water locked away in rocks though, to my understanding the majority of the water is in the mantle and not even the oceans, but my source is my butt for that one

Earth isn't even really a "rock", it's mostly a ball of iron.

It's a ball of iron covered with rocks (i.e. metal oxides) cover with water (i.e. hydrogen oxide).

I don't buy it. Even allowing counting iron as separate from what rocks can be composed of (and using mass instead of volume) you still have 30.1%+15.1%=45.2% of the Earth as oxygen and silicon (which are most certainly part of what makes a rock) at which point you've already disproved the claim Earth is more a ball of iron than a ball of rock.

A ball of iron covered with a ball of rocks is a more fair statement though, and I'd agree with that. It's just that center ball isn't most of what makes up the Earth (by any measure).

Oceanus's ocean tosses with slow, tall waves, beneath a pale blue sky. The colonists live in tall cities of steel and concrete with buildings sealed against the planet's harsh environment, on platforms floating on the planet-wide ocean. They spend their time pursuing art, leisure, and spiritual fulfilment, while automatic machines take care of their material needs.

If you could squeeze the Earth's atmosphere into a ball of similar density it would be more or less of size of the middle sphere (all the oceans only weigh 270 times as much as the atmosphere [1]).

So there you have it: the key ingredients all life depends on are but a tiny boundary layer of water and air, stretched thinly between solid rock and the hostile emptiness of outer space.

The grand challenge of our sustainability is, indeed, how much can we (humans) perturb this extraordinary complex boundary layer without inducing runaway dynamics that we (or rather, future generations of us) will not particularly like.

[1] https://www.sciencefocus.com/science/how-much-does-earths-at...

I don't really follow a lot of comments questioning the choice of shape, methodology, exclusion of water in the mantle etc.

I believe the purpose of the image is to evoke sense of preciousness and responsibility towards the water we have - maybe how much for granted we take our "blue planet".

To me, this is an amazingly effective and visually poignant way of doing just that.

Yep, it's quite misleading since the region where they looked for water at all is an incredibly thin layer on the outside of the planet, but they show it all as if it applied to all of the volume.

It's not bad on purpose if that what you understood.

But the comments here are full of "it's so little!" variants, where if you took the rest of the Crust and smashed as a sphere, it wouldn't be much larger than the water one.

It did evidently mislead a large number of people.

Geologically it probably isn’t. If all surface oceans disappeared, some of that water would likely come out to the surface and form new bodies of water, over millions of years.

Depends on the temperature. At Earth-like temperatures, yes, it would. The transition between the two is around 175 K, give or take; below about 150 K ice is quite stable in a vacuum even over astronomical timescales; above 200 K it sublimates rapidly. (Surface liquid water is never stable in a vacuum or thin atmosphere regardless.)

The rate of evaporation ramps up exponentially, from ~irrelevant at the bottom of that range to fast at the top. (For a body of this size, any resulting vapor would be quickly lost at these temperatures, so the rate of evaporation is effectively the rate of water loss as well.)

This is why Jupiter can have icy moons (temperature ~100 K), but ice sublimates quickly on Mars (~200 K).

Going from a liquid to a gas takes energy, which rapidly lowers the temperature of what remains. Net result most of the water freezes without some external energy source. Sublimation then lowers the temperature of the ice until near absolute zero, again unless there’s some external energy source.

i knew there would be someone to just try to get out of the answer by failing to just go with the spirit of the question by being pedantic. even my own attempt at dispel pedantry just allowed for even more pedantry.

I don't know what you wanted.

If you wanted to ask whether that amount can hold together and become spherical, then just by comparing to Ceres doesn't that make it plenty?

It's not crazy to interpret "hold itself together" as more complex and including vapor escape.

The freezing-into-a-ball-of-ice is relevant here. A body that small can't hold on to water vapor at anything a human would consider a reasonable temperature; the average velocity of light gases at human-sane temperatures is high enough to overcome their escape velocity. See [1] for a log-log plot of what gases a body can hold onto - even Mars, which is much larger and denser than a Ceres-sized ball of water, has lost most of its water (although other factors like the solar wind are contributors there).

A cold enough body, though, has a low enough vapor pressure that this isn't relevant even over cosmological timescales. That's why Europa can can have a stable icy surface. It's far enough from the Sun (and has a low enough albedo) that it's very very cold (about 100K), and at that temperature ice doesn't sublimate very much.

TLDR: a Ceres-sized ball of water could hold itself together, but only as long as it stayed water. But it wouldn't be able to. Either it'd be cold enough to freeze over at the surface, or hot enough to evaporate into vapor that would escape.

[1] https://en.wikipedia.org/wiki/Atmosphere#/media/File:Solar_s...

Given that water gets lighter when cooling down right above its fusion temperature, and that ice is a pretty good insulator. You'd have liquid water below an ice crust for a lot of time. It would eventually freeze entirely and be slowly eaten by the Sun's radiations. But that would take a pretty long time (well on a human scale).

Yeah, that's why I specified freeze over and not freeze through, although without doing the math I'm pretty sure it'd still freeze through on solar system timescales without radioactive (as in Earth's own mantle's case) or tidal (Enceladus, Europa, possibly Triton and Ganymede) heating.

The sphere of water would have a surface gravity of 0.016 g, 1.6% of Earth's gravity, 1/10th of the Moon's gravity. So yes, it would gravitate into a ball shape, aside from slowly boiling off if it's inside the orbit of Mars (our 32°F Goldilocks Zone) or freezing if it's farther out.

It would make Mars warmer. It would melt all the ice and CO2. It would give Mars an ocean. Of liquid rock. This is assuming that it doesn't destroy Mars completely. There might be enough fragments to make Solar System dangerous place and destroy life on Earth.

Europa is the size of our Moon. Colliding it with Mars would be similar to the collision that formed our Moon.

At some point I saw a design for a machine you could park at the Lagrange point between Mars and the Sun that would collect solar power and spit out a magnetic field strong enough to deflect enough of the solar winds that we wouldn't need to worry about that.

If we had the technology allowing us to move a full satellite through the solar system, we could probably do it in a way that would just make Mars a bit closer to the sun so that the weather gets nicer (sure, if it gets too close to earth it's going to mess up with both orbits, but we can as well correct it when it happens, right?)

Just a few quick calculations to make it more relatable...

They say the smallest sphere of freshwater lakes and rivers amounts to 93,113 cu km. There are 1 bil cu m per cu km. With a global population of 8.2 bil people, that comes to 11,355 cu m per person. That's a 22.5 meter wide/deep/tall cube (or about 7 or 8 stories tall building).

If we use the sphere that includes groundwater, 10,633,450 cu km. Then we end up with 1,296,762 cu m or a 109m wide cube per person.

> The largest sphere represents all of Earth's water. Its diameter is about 860 miles

Should be a radius of 430 miles, no?

The image is very non-intuitive, IMO, because it's making the water appear so small compared to the entire planet (which, duh, obviously the water is only part of earth), but also drawing the planet that small really hides how friggin big the earth is!

Helped for me to compare to the moon. The water sphere has less than half the radius of the moon (~1080 miles). Think that’s roughly 7-8% of the moon’s volume if it were a perfect sphere.

Yes. The fresh-water lakes and rivers sphere definitely does not look like it could fill the Great Lakes next to it. I am not saying it doesn't, I'm just saying it doesn't look like it could.

Average depth of Lake Michigan is around 300 feet. Longest dimension is about 300 miles. If you drew a map of Lake Michigan on a sheet of letter-sized paper, the paper would be thicker than the average depth of water.

I thought the border with space is generally (and arbitrarily) said to be the Kármán Line, at 100 km / 62.1 mi. I'm not nitpicking, just curious about other definitions.

Also, I thought LEO typically begins around 180 km / 112 mi.

It's interesting to consider that there's about 26,000,000 km^3 of ice in the Antarctic ice sheet, which would give you a much larger ~150 m^3 cube of ice per person. That's not including the Greenland ice sheet or any sea ice.

Turn Randall Munroe loose on this idea and be prepared for unspeakable devastation as a tsunami of Lovecraftian proportions wreaks havoc on the planet...

It would be nice to see the "carbon" version of this infography. How much carbon is in the atmosphere as CO_2, in the biosphere as part of living stuff, and buried kilometers underground as gas and oil. Also, how much of that carbon we are pumping per year from underground to the atmosphere+biosphere system, and vice-versa.

I think it’s important to keep in mind that if you did this same visualization on a planet with ten times Earth’s radius, but the same ocean depth and water distribution, then the water blobs would seem even smaller in comparison to the planet.

I’m just not sure it’s a particularly useful illustration to compare the volume of water on a planet to that of the planet itself.

Why is this confusing? We aren't comparing planets by amount of water they have. I thought the goal of this visualization was just to make a point - the amount of fresh water in rivers and lakes appears to be the size of a large metropolis in radius. Seems like a cool way to show scale of water resources

I think this is kind of useless information unless presented with other spheres for humans, structures, animals, plants, forests etc. for comparison. And ants.

This was my first thought too.

I had no idea where to start. ChatGPT had a rather impressive looking “proof of work” that put all living humans into a 976m-diameter sphere, compared to the ~1384km-diameter sphere. Ie ~1km human sphere and 1,384km water sphere.

The water spheres look small but here's a fun back-of-the-envelope computation. The article states there is 22.3k mi^3 of water in lakes and rivers. One person in the USA (a high consumer) consumes 82 gallons of water every day (source: epa.gov) which is 7.4E-11 mi^3. Let's say each person does this for a long-lived 100 years, giving 7.4E-9 mi^3 per lifetime. So the 22.3k mi^3 of lake and river water can support 3 trillion lifetimes. That's not including the much larger amounts of ground water and ocean water. Those "small spheres" are huge!

This is similar to the idea that if you scaled the Earth to the size of a standard size 5 football and dried it off, you would barely be able to feel the mountains or trenches on the surface. The water is therefore a very thin film over the land in those terms.

Not sure this is accurate as we've discovered that water can reside deeper in the Earth than previously imagined and in addition to that the density of water at the surface is different than at the bottom of the ocean. I suppose they are also accounting for the salt being removed too. But my argument is probably in the margin of error so what do I know?

https://www.technology.org/how-and-why/what-would-happen-if-....

So I feel like the USGS is exagerated.

The density of water at the bottom of the ocean is actually quite similar to the density on the surface; it differs by only a few percent. Gases compress proportionally to pressure, but liquids act more similar to solids and compress very little even under enormous pressures.

The oceans are only about 3.5% salt by weight, so that doesn't make a huge difference, either.

I was curious how much of this water we lose to space via evaporation. Looking around, apparently not much; only few molecules achieve escape velocity. But can't find a good calculation yet.

The World Gold Council says:

> If every single ounce of this gold were placed next to each other, the resulting cube of pure gold would only measure around 22 metres on each side

So that can't possibly be right, you must be off by a factor of 10 or so at least—Wolfram Alpha says a 30m diameter sphere.

27 meter diameter in fact. A 27-meter sphere is about 150 times as voluminous as a 5-meter sphere.

It's still a mind bogglingly small amount considering that humans have spared no toil, sweat and blood on industrial scale gold mining ever since the dawn of written history - and since gold is so valuable and hard to destroy, most of it should still exist to this day in form or another.

Yet, if you smelted it all to a single object it would fit on a typical single family housing plot.

Spheres/circles are definitely surprising in how a seemingly small increase in radius changes the volume/area much more drastically. The cubing/squaring exponent is easily taken for granted.

From TFA: "This sphere includes all of the water in the oceans, ice caps, lakes, rivers, groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant."

> This sphere includes all of the water in the oceans, ice caps, lakes, rivers, groundwater, atmospheric water, and even the water in you, your dog, and your tomato plant.

I would like to have a zoomed-in picture of that 'tiny' freshwater lakes and rivers to see its height. From this perspective, it doesn’t add up. Just above it, the Great Lakes look far bigger, not to mention other lakes and rivers in the world.

The Great Lakes span across hundreds of miles, but the deepest point is less than a quarter mile, and most of it is much shallower than that. I.e., it's a super thin film over that big surface area.

"Yes, Lake Michigan looks way bigger than this sphere, but you have to try to imagine a bubble almost 35 miles high—whereas the average depth of Lake Michigan is less than 300 feet (91 meters)"

As an aside, the smallest ball is a few hours travel by bicycle, or two days on foot. Planet Earth is large, but it brought home how it is not so large. I would have guessed that 35 miles was a lot smaller than is shown.

Ok I don't mean to be pedanntic but a sphere is just the boundary of a ball. If we are trying to capture volume we should be talking about balls of water.

I agree. It's a volume of water bounded by a sphere. I'm just being pedantic about the common use of the word in this thread.

I'm also somewhat surprised no one else was being pedantic about this. I expect better from HN :)

I'm aware, notice my comment specifically states "the Earth's *surface* " not just "the Earth". However, my kitchen counter is a flat surface, it's common knowledge the Earth isn't flat and the average ocean depth is 3,682 meters

The earth is smoother than a billiard ball when accounting for relative size. Highly likely the earth is actually flatter than your countertop when accounting for size.

That was my point. The Earth isn't flat, but its surface is very smooth.

You give the average ocean depth at 3.7km, but the Earth's diameter is about 12,742km, making those bumps pretty insignificant. If you cover your countertop in sandpaper and spill water on it, the difference in coverage going to be almost negligible.

What a coincidence, One hour before reading this article I was thinking of it! I was imagining that how the sphere will look like if made of oceans and seas' water. Now I got to know it :D

We always talk about how scarce freshwater is but this image reprenstation has made it difficult to imagine how much supply do we have for an ever growing human population, the growing demand for water and how long will it last.

It's more extreme than that, it stops existing.

The comment you're replying to is about fresh water. Which becomes non-fresh when it mixes into seawater or waste or pollution. No need to leave the Earth.

Admittedly, it's probably better to talk about the cycle, since non-freshwater will be automatically converted back to freshwater via solar energy. But the rate can be slowed—eg, dump a bunch of toxic stuff in one place, it'll drain to a river, now everything from that point and downstream is no longer freshwater. Or pump up enough groundwater. Or inject toxic crap down where the groundwater lives.

We're quite good at reducing the total amount of freshwater available.

Spheres could be a more viable unit of measurement instead of "Millions of Gallons".

Imagine the headline:

  500 million gallons of water expected to melt this year

VS

  1.2 microspheres of seawater expected to melt this year

That's actually a lot bigger than I thought - The largest asteroid Ceres would be 1/3 the diameter of this water sphere (860mi)

That's a LOT of water.

IIRC water in earth's mantle is magnitudes greater than the volume contained in our oceans. I think only part of Earth's H2O story is illustrated by this graphic.

Anyone remember that Voyager episode where they find this exact thing floating in space, held together by some kind of gravity generator? The plot was forgettable but the concept was super interesting.

Sounds like the water moon from Iain M Banks "The Algebraist", quote:

"I was born on a water moon.

Some people, especially its inhabitants, called it a planet, but as it was only a little over two hundred kilometers in diameter 'moon' seems the more accurate term. The moon was made entirely of water, by which I mean it was a globe that not only had no land, but no rock either, a sphere with no solid core at all, just water, all the way down to the very center of the globe.

If it had been much bigger the moon would have had a core of ice, for water, though supposedly incompressible, is not entirely so, and will change under extremes of pressure to become ice. (If you are used to living on a planet where ice floats on the surface of water, this seems odd and even wrong, but nevertheless it is the case.) This moon was not quite of a size for an ice core to form, and therefore one could, if one was sufficiently hardy, and adequately proof against the water pressure, make one's way down, through the increasing weight of water above, to the very center of the moon.

Where a strange thing happened.

For here, at the very center of this watery globe, there seemed to be no gravity. There was colossal pressure, certainly, pressing in from every side, but one was in effect weightless (on the outside of a planet, moon, or other body, watery or not, one is always being pulled towards its center; once at its center one is being pulled equally in all directions), and indeed the pressure around one was, for the same reason, not quite as great as one might have expected it to be, given the mass of the water that the moon was made up from."

IIR, the Earth's mantle is understood to contain several times the total water content of the oceans, glaciers, lakes, etc.

Obviously that water would be somewhat less accessible and quantifiable, but...

Anyone familiar with the current geoscience on this?

> The blue sphere over Kentucky represents the world's liquid fresh water (groundwater, lakes, swamp water, and rivers).

So the medium blue sphere includes groundwater and swamp water while the tiny dot does not.

I think that part of what is surprising is that our brains cannot comprehend the scale of earth so we see the photo as a model of earth and wonder how it's possible that so little water can spread throughout. At model scale, the water wouldn't spread all the way around the globe because of viscosity and surface tension.

Ceres could be taken apart with solar energy and rebuilt into a habitat much bigger than the Earth, never mind Mars. Ceres leads to the stars, Mars is just a dead end.

Is there reason to believe the stars are less of a dead end than Mars? It's easy to imagine us making a huge bet on interstellar travel, and just dying in interstellar space. Surely there's untold abundance in the stars, but if you can't actually reach it, then it may as well be a mirage.

Whenever I consider the possibility of interplanetary colonization, I come back to the conclusion that the only way to make it feasible is to reorient our economy towards sustainability in order to survive on Earth indefinitely. It's going to take a long, long time to develop the required technology, there's no real reason to believe artificial terraforming is even possible (since our sample size is 0), and even if it is it may take thousands or millions of years to complete.

I'm not being facetious with that last part, in the absence of information to the contrary, we should expect technology that works via geologic processes to run on a geologic timescale. I personally think artificial terraforming is probably possible, and that we could accelerate it to be much faster than the natural terraforming of Earth. But accelerating a 2 billion year process to be 10000x faster still takes 200k years. (ETA: I suppose a lot of that was the planet forming and the rate of bombardment falling to something tolerable, which eg Mars was already subject to, so maybe call it 1B/100k years.)

I did a lot of analysis for the problem of "build a solar sail factory on a carbonaceous chondrite asteroid that makes sunshades to deploy at the L1 point", particularly from a chemical engineering point of view.

One interesting thing was that a lot of the chemistry involved was similar to the chemistry of decarbonization and carbon capture, particularly when you get CO2 as a waste product it is too precious to vent so you are going to feed it back into your "petrochemical" line.

Objects like Ceres are the norm once you get out to the outer solar system, the difference is that Ceres is close enough to the sun for solar energy to be a good power source. Centaur objects, the moons of outer planets, and Kuiper belt objects like Pluto are similar but when you get far from the Sun you need to use a different power source such as D-D fusion.

If a species became independent of sunlight it could take advantage of very generic objects that exist throughout interstellar space (comets, rouge planets, etc.) and make the journey in hops of (say) 100 years from one object to another. At that rate it would be possible to visit another star system in 10,000 years with a comfortable lifestyle. People like that might as well keep comet hopping but if they came across a star system I'd imagine they start some project like a Ceres megastructure because it is generic you can find some object like that and be able to establish a huge industrial base and population larger than the Earth with the same head end you've used all this time and same comfortable lifestyle.

Earth would be priority two if that for those people. Grabby aliens might have disrupted Ceres but left the dinosaurs alone. But Ceres is here, so they were not. Ceres is such an attractive target that it should be a SETI goal to look for hardware left behind. Would be hilarious if they stole the Deuterium.

It's interesting speculation. I just can't accept the existence of a spacecraft that can last 100 years without a catastrophic failure, or Ceres being reforged into a factory, or a nation of people who live entirely independent of Earth until I see it.

Sometimes people talk about these things as if they are inevitable, but I would say there's an extremely good chance we go extinct without ever leaving this solar system (Voyager 1 notwithstanding). I think this is a valuable and grounding perspective in planning for the long term future of humanity, because we have to accept that that future takes place here on Earth and largely with the technology we already have. Space colonization is seductive, but like all silver bullets, impossible to operationalize within the constraints imposed on us by our situation.

But it's probably not a useful one when picking SETI targets or generating other research ideas, and that stands on it's own merit.

Assuming you mean "the depth of this water, if confined to a cross-sectional area the size of the United States", this is one of those nice Fermi estimation problems:

- I know the US contains hundreds of millions of people, and the world contains a single-digit number of billions. So the US has about 10% of the world's people.

- The US probably isn't particularly dense or sparse relative to other populated areas, so 1/10 the population should be 1/10 the Earth's land area.

- The Earth has twice as much ocean as land, and

- The ocean is a few miles deep - let's say 5 - so there's about 10 miles of ocean depth per land area.

- So compressing that to 1/10th the land area suggests the oceans should cover the US to a depth of about 100 miles.

The exact answer, it turns out, is about 89 miles - really close, without looking up a single piece of information!

https://www.wolframalpha.com/input?i=%28332%2C500%2C000+cubi...

I'm trying to visualize the amount of water here, but it's hopeless unless an elementary student can calculate how many oil drums it would fill or football fields it would cover to a depth of one yard.

The problem with this sphere is that people are terrible at understanding the mind boggling scale represented by "height" here. It looks like a tiny drop that "fits on the US". Instead it has a diameter of 860 miles. That's a ball of water that reaches all the way to outer space...

...and then keeps going for another 800 miles.

They're comparing the sphere of water to the Earth which is a sphere.

Also it's by the Water Science School, so it doesn't seem your definition of completeness was the intention.

Humans are notoriously terrible about estimating volumes when things are curved and volume functions are exponential.

A great example of this done in 8th grade science classes across the US is to put 100ml of water in a 100ml graduated cylinder, 150ml in a 1L beaker, and ask the class which has more. Humans are awful at estimating how much volume the increased radius adds, and usually will say the 100ml.

The problem only gets worse as we graduate from cylinders to spheres.

We can all visually see which sphere is bigger, but cannot come close to estimating how much bigger one is than another.

Already eight years ago, I complained that people were using "exponential" where it doesn't make any sense. (See these two data points? Clearly exponential growth happend there. They're so far apart!)

I believe the problem has increased exponentially since then. Now everyone is using exponentially in literally the same way as literally.

I'm not sure if you are kidding but just in case you are not this is very misleading and in fact misguided.

Refering to polynomials as exponential just results in confusion essentially removing any meaning from the word. Any function can be written as something involving exponents, so that statement becomes meaningless.

> They are polynomial

I don't think this word means what you think it does. Or I don't. Exponents are just the number the value is raised. Squaring a value just uses an exponent of 2 where cubing uses an exponent of 3. Polynomials are x^2 + x + 1 type of equations. But admittedly, it has been 30+ years since I've thought about them at that level, so maybe I'm the one with fuzzy groking

"Polynomial" meaning x^n. "Exponential" meaning e^x.

Exponentials eventually grow much faster than polynomials, no matter what the exponent is.

I mean, look, in v = x^3, the "3" is an exponent. But it's not an exponential function because the variable isn't in the exponent.

> Exponentials eventually grow much faster than polynomials, no matter what the exponent is.

Since we're being pedantic, that last clause should be: "as long as the exponent is greater than 1."

We could, but I would describe it as "mathematically accurate". Which is not incompatible with "unreasonably narrow", given that the definition of "exponential" has recently gotten polluted enough that it is now often synonymous with "fast growing". But what's the point of arguing over definitions if we're going to start with a baseline of saying that there is no basis upon which to argue definitions other than recent conventional usage?

> there are others which allow x^2 to be described as "exponential".

Those same definitions allow x*1000 to be described as "exponential". (x*1000000 would be "more exponential"!)

If you're describing something as exponential, then either you're just saying "fast growing", or you're trying to describe the type of growth. If you're describing the type of growth, then neither x*1000 nor x^2 is exponential. The fact that x^2 has an exponent in it is no more relevant than saying that x*1000=x*10^3 and x*10^3 has an exponent in it.

(Again, I sadly accept that in today's world, "exponentially" is being used to mean "fast growing", or sometimes more specifically "faster than linear". If I'm trying to understand what someone means, then it doesn't matter whether I find that usage to be a good idea or not.)

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